Analysis, Design and Experimental Assessment of a High Power Density Ceramic DC-Link Capacitor for a 800 V 550 kVA Electric Vehicle Drive Inverter

The drive inverter is a crucial component of an electric vehicle (EV) powertrain, being responsible for the DC/AC power conversion between the battery and the electric motor. The increasing demand for lower weight and higher conversion efficiency is opening new challenges, encouraging the adoption of new technologies (e.g., wide bandgap semiconductor devices). In particular, the DC-link capacitor typically represents the bulkiest inverter component, posing a strict limitation to the achievable converter power density and thus being subject to great pressure for improvement. In this context, novel ceramic capacitor technologies (e.g., PLZT) promise superior performance with respect to well established film-based solutions, featuring both higher specific capacitance and higher RMS current capability. Therefore, this paper focuses on the analysis, sizing, design, and experimental assessment of a PLZT-based ceramic DC-link capacitor for next-generation EV drive inverters, including a comparative assessment with a state-of-the-art film-based solution. In particular, in view of the non-linear behavior of the PLZT capacitance value with respect to the DC-bias voltage and the amplitude of the excitation, a novel correlation between the effective large-signal capacitance and the peak-to-peak voltage ripple is derived experimentally, providing useful information for the DC-link capacitor sizing (i.e., not available from the capacitor manufacturer). For verification purposes, a full-scale DC-link capacitor prototype for a SiC MOSFET 800V, 550 kVA, 20 kHz drive inverter is realized, demonstrating superior power density (i.e., ≈ two thirds smaller and ≈ one third lighter than a corresponding film-based solution). Finally, the inverter prototype is also exploited to validate experimentally the proposed DC-link peak-to-peak voltage ripple estimation procedure, based on the newly obtained large-signal capacitance characterization.